New Phase Transitions of Monoclinic RbD2PO4 and Its Forced Transition to the Ferroelectric State

Dielectric and dilatometric properties of monoclinic RbD 2 PO 4 have been studied. The crystal undergoes successive phase transitions accompanied with a large peak of the dielectric constant along the unique b axis ε b at 44°C ( T II ), and a change in temperature gradient of ε b -1 at 104°C ( T I ) respectively. The phase below T II is antiferroelectric or approximately antiferroelectric. The forced transition to a ferroelectric phase is observed below T II as a double hysteresis loop. The critical electric field to cause the forced transition and spontaneous polarization of a sublattice are about 12 kV/cm and 1.8 µC/cm 2 at 30°C respectively.